Reduction of PAH and soot in premixed ethylene-air flames by addition of dimethyl ether

Results are presented from a combined experimental and modeling study undertaken to understand the pathways by which the addition of dimethyl ether ( DME) to fuel- rich ethylene flames causes reductions in PAH and soot. The experimental work was conducted in a flat- flame burner at equivalence ratios of 2.34 and 2.64. DME was added to the ethylene at two levels corresponding to 5 and 10% oxygen by weight in the fuel. Soot was measured by laser- induced incandescence calibrated with light extinction, and aromatic species were measured using laser- induced fluorescence. Modeling was based on a 1D, premixed flame model and kinetic mechanisms described in the literature. The modeling work captures the trends in aromatic species with changes in equivalence ratio and oxygen concentration in the fuel. However, the soot predictions do not match the increases observed at the higher equivalence ratio. Analysis of the modeling results for the lower equivalence ratio shows that the addition of DME to the ethylene reduces the aromatic species by increasing the concentration of oxidizing radicals, OH and O, and by reducing the amount of carbon that is available to form precursor species.